Introduction to Electronics
EHB222E
Grading
Grading: Two midterm exams (each 30%) and one final exam
(40%).
Midterm exams: 4th of April and 16th of May
Before the final exam the sum of your midterm exam grades
should be larger than 50 (MT1+MT2} ≥ 50).
Introduction to Electronics
➢
Introduction
➢
Semiconductors & Doping, Basics of pn junction
➢
Diodes
➢
BJT Transistors
➢
MOSFET Transistors
➢
Operational Amplifiers
What is Electricity?
Atoms contain
1. Protons (+)
2. Neutrons (0)
3. Electrons (-)
Electricity is generated from the motion of tiny
charged atomic particles called electrons and
protons!
The unit of charge is Coulomb (C)
Protons are positively charged and electrons are negatively charged.
Law of Electric Charges
The law of electric charges states
that like charges repel, and opposite
charges attract.
Protons are positively charged and
electrons are negatively charged, so they
are attracted to each other.
What is Voltage?
- measured in volts.
Voltage is the difference in energy level from one end of the battery
(or any other energy source) to the other.
The energy difference causes the negative charges to move from a
lover voltage level to higher voltage in a closed circuit.
6
A battery in an electrical circuit plays the
same role as a pump in a water system.
A battery establishes a difference
A battery pushes the
of potential that can pump electrons. electrons through the
conductor.
7
Current
➢ Current is the amount of electric charge (coulombs)
flowing through a cross section of a conductor in one
second.
1 Ampere = 1 Coulomb/second
➢ Electron flow is from a lower potential (voltage) to a
higher potential (voltage).
➢ Current flow is from a higher potential (voltage) to a
lower potential (voltage).
higher potential
Direction of
current flow
lower potential
8
Sign Convention for Current Flow
• Electrons carry negative charge
• Current flow is in opposite direction
- - - - - -- - - - - - - - - - - - - - - - - electron motion
Current direction
9
Current Flow
• The direction of current flow is indicated by an arrow.
DC Voltage
Source
+_
higher potential
Current flow is from a higher potential (voltage) to a lower
potential (voltage).
Note: The voltage sources in the circuit flow current through
nodes and wires.
10
Electric Circuit
Intersection
point of wires is
call as a node
A single node
Conducting
wires
If two or more nodes are
connected just by wires,
intersection point can be
considered as one single
node.
Nodes are Connected
by Wires Only
One big node
+_
Group of nodes
Oneconnected
big node only by wires
Electronic
elements
11
From Conservation of Charge
Current is the amount of electric charge (coulombs)
flowing through a cross section of a conductor in one
second.
The sum of charges flowing into a node
must be equal to the sum of the
charges flowing out of the node.
I1 = I2 + I3
Diagram “b” shows a
mechanical analogy
Kirchhoff’s Current Law
• The sum of currents flowing into a node
must be balanced by the sum of currents
flowing out of the node.
i1
node
i2
+_
i1 flows into the node
i2 flows out of the node
i3 flows out of the node
i3
Gustav Kirchoff
was an 18th century
German
mathematician
i1 = i2 + i3
13
Sometimes Kirchhoff’s Current Law is
abbreviated just by
KCL
Review: Different ways to state KCL:
✓ The sum of all currents entering a node must be zero.
✓ The net current entering a node must be zero.
✓ Whatever flows into a node must come out.
14
Voltage (Difference in energy level )
• Voltages are measured across the nodes of a circuit.
• The direction of a voltage is indicated by + and – signs.
+
v1
–
+
+_
v2 –
+
v3
–
+
v4
–
higher potential
lower potential
15
Kirchhoff’s Voltage Law
The voltage measured between any two nodes does not
depend of the path taken.
voltage
+
+
v1
–
+
_
Example of KVL:
Similarly:
and:
voltage
v2 –
+
v3
–
voltage
+
v4
–
v1= v2 + v3
v1= v2 + v4
v3= v4
16
Using the Formal Definition of KVL
“The sum of voltages around a closed loop is zero.”
• Define an arrow direction around a closed loop.
• Sum the voltages that are encountered around the loop.
• If the arrow first encounters a plus sign, enter that voltage with a
(+) into the KVL equation.
• If the arrow first encounters a minus sign, enter that voltage with a
(–) into the KVL equation.
+
v1
–
+
+_
For the inner loop :
For the outer loop:
v2 –
+
v3
–
–v1 + v2 + v3 = 0
–v4 – v2 + v1 = 0
+
v4
–
17
Electronic Circuits
Circuits are obtained by connecting electronic elements
Typical electronic elements are
•diodes
•resistors,
•capacitors,
•inductors
18
Ohm’s Law & Resistors
Let us remind the Ohm’s Law
V
+
_
V
I = ——
R
V
R = ——
I
Georg Ohm
• Assume that the wires are “perfect conductors”
• The unknown circuit element limits the flow
of current.
• The resistive element has resistance R
19
Ohm’s Law
Voltage drop across a resistor is proportional to the current
flowing through the resistor
v = iR
If the resistor is a perfect conductor (or a short
circuit)
R = 0Ω, then
v = iR = 0 V
no matter how much current is flowing through
the resistor
Resistors in Series
v = iR
Resistors in Parallel
V
I = ——
R
Resistors in Parallel
(Conductance: G = 1/R)
Voltage Divider
Equivalent
Resistance –
Complex Circuit
Example: Calculate the current which is flowing through R4.
CAPACITOR
Energy Storage Device
The Capacitor
Capacitors are one of the fundamental passive components. In its
most basic form, it is composed of two conducting plates
separated by a dielectric material.
The ability to store charge is the definition of capacitance.
Conductors
Dielectric
𝑄
𝐶 = ; 𝑈𝑛𝑖𝑡 : 𝐹𝑎𝑟𝑎𝑑 = 𝐶𝑜𝑢𝑙𝑜𝑚𝑏𝑠 𝑝𝑒𝑟 𝑣𝑜𝑙𝑡
𝑉
Dielec tric
Leads
Initially uncharged
capacitor
A
−
+
−
+
−
+
−
+
+
−
+
+
−
+
Plates
− Elec trons
B
−
Charging
−
−
+
+
−
−
+
+
−
−
+
A +
−
−
−
−
−
+
−
− +
−
−
−
−
−
B
−
−
−
VS
Fully
charged
−
−
−
−
−
−
−
−
−
−
−
+
+
+
+
+
+
+
+
+
+
A +
+
B
−
After fully charged, a capacitor behaves as an open circuit
and does not allow current flow.
VS
Source
removed
+
+
+
+
+
+
+
+
+
+
A +
−
−
−
−
−
−
−
−
−
−
− B
A capacitor with stored charge can act as a
temporary battery.
Both the voltage and current have an
exponential forms
•C, capacitance, has the unit of Farad (F)
1 F = 1 A.sn/V
Example
Find the voltage across R1. Note that the polarity of the
voltage has been assigned in the circuit schematic.
First, define a loop that include R1.
Example (con’t)
There are three possible loops in this circuit. Only two of
them include R1. Either loop may be used to determine VR1.
Example (con’t)
If the outer loop is used, follow the loop clockwise.
Example (con’t)
Follow the loop in a clockwise direction.
 The 5V drop across V1 is a voltage rise.
 VR1 should be treated as a voltage rise.
 The loop enters on the positive side of the CURRENT source and
exits out the negative side. This is a voltage drop as the voltage
becomes less positive as you move through the component.
−5V − VR1 + 3V = 0
VR1 = −2V
Example (con’t)
Suppose you choose the green loop instead.
Since R2 is in parallel with I1, the voltage drop across R2 is
also 3V.
Example (con’t)
Follow the loop in a clockwise direction.
 The 5V drop across V1 is a voltage rise.
 VR1 should be treated as a voltage rise.
 The loop enters R2 on the positive side and exits out the negative
side. This is a voltage drop as the voltage becomes less positive
as you move through the component.
−5V − VR1 + 3V = 0
VR1 = −2V